Drug Interactions between Nuedexta and pirfenidone

GENERALLY AVOID: Coadministration with potent CYP450 2D6 inhibitors (e.g., quinidine, terbinafine) may significantly increase the plasma concentrations of dextromethorphan in patients who are extensive metabolizers of this isoenzyme (approximately 93% of Caucasians and more than 98% of Asians and individuals of African descent). The proposed mechanism is inhibition of the CYP450 2D6-mediated O-demethylation of dextromethorphan. Studies in humans have shown an increase in systemic exposure of dextromethorphan of up to 43-fold when given concurrently with quinidine. Increased plasma concentrations increase the risk of dextromethorphan-related adverse effects (e.g., agitation, confusion, tremor, insomnia, diarrhea, and respiratory depression) and serotonin syndrome. However, this interaction has also been used clinically, with dextromethorphan in combination with quinidine indicated by some authorities for the treatment of pseudobulbar affect. Data evaluating the impact of this interaction in patients who are poor metabolizers of CYP450 2D6 are limited; most studies include extensive metabolizers of this isoenzyme. It is expected that poor metabolizers would have elevated dextromethorphan levels without concurrent quinidine

MANAGEMENT: The combination of dextromethorphan with potent CYP450 2D6 inhibitors should be generally avoided. Some manufacturers consider the concomitant use of dextromethorphan and selective serotonin reuptake inhibitors contraindicated. If use is considered necessary, the patient should be monitored for signs of dextromethorphan adverse effects (e.g., agitation, confusion, tremor, insomnia, diarrhea, and respiratory depression) and serotonin syndrome, and advised to notify their health care professional if these adverse effects develop or worsen. Dose reduction of dextromethorphan may also be required.

MONITOR: Coadministration with moderate or potent inhibitors of CYP450 2C9, 2C19, 2D6, and/or 2E1 may increase the plasma concentrations of pirfenidone, especially when used in addition to a moderate or potent CYP450 1A2 inhibitor. Pirfenidone is primarily (70% to 80%) metabolized by CYP450 1A2, with minor contribution from CYP450 2C9, 2C19, 2D6, and 2E1. In 25 healthy nonsmokers and 25 smokers who were administered a single dose of pirfenidone with the potent CYP450 1A2 inhibitor fluvoxamine (50 mg at bedtime for 3 days; 50 mg twice a day for 3 days; then 50 mg in the morning and 100 mg at bedtime for 4 days), pirfenidone systemic exposure (AUC) increased approximately 4-fold in nonsmoking subjects and 7-fold in smoking subjects. Fluvoxamine also inhibits CYP450 2C9, 2C19 and 2D6, although the extent to which these effects contribute to the interaction has not been established. The interaction has not been studied with specific inhibitors of other isoenzymes involved in the metabolism of pirfenidone.

MANAGEMENT: Concomitant use of pirfenidone with moderate or potent inhibitors of CYP450 2C9, 2C19, 2D6, and/or 2E1 in addition to a moderate or potent inhibitor of CYP450 1A2 (e.g., certain fluoroquinolones, oral contraceptives, deferasirox, methoxsalen, mexiletine, thiabendazole, ticlopidine, zileuton) should be avoided. No particular precaution is necessary if pirfenidone and CYP450 2C9, 2C19, 2D6, and/or 2E1 inhibitors are coadministered without a moderate or potent CYP450 1A2 inhibitor. However, a prolonged duration of monitoring for adverse effects may be required depending on the elimination half-life of the concomitant drug. For example, it should be noted that rolapitant, a moderate CYP450 2D6 inhibitor, may increase plasma concentrations and the risk of adverse effects of pirfenidone for at least 28 days after administration of rolapitant.